Kalshi and Polymarket are the two biggest prediction markets by trading volume and attention. They solve the same problem — letting you price probabilities directly as event contracts — but they do it through very different structures. One is a CFTC-regulated US exchange. The other is really two venues — a CFTC-designated US exchange settling in dollars, and a separate USDC-based international book that is closed to US persons.
Here is the comparison that actually matters for a real trader in 2026.
> Market snapshot — last updated May 25, 2026. Kalshi crossed $2B in cumulative contract volume in Q1 2026 per the CFTC swaps data repository feeds, with daily turnover concentrated in the FOMC, CPI, and World Cup 2026 books. Polymarket cleared more than $3.6B during the 2024 US election cycle (the largest single-event volume in prediction-market history, per Polymarket's public stats page) and remains the deeper book on 2028 cabinet, global soccer, and crypto-price futures — though that volume ran on its international book, which is closed to US persons. US traders now have four venues: Kalshi, DraftKings Predictions, FanDuel Predicts, and Polymarket US, which opened in December 2025.
Short answer up front
If you are a US resident, we still default to Kalshi — but on coverage and economics, not legality. Kalshi lists a far broader set of contracts and reaches all 50 states. Polymarket US is a legitimate second venue, open to US traders since December 2025, with a narrower slate and state-by-state availability. Full context in the Polymarket US guide.
Outside the US, the answer depends on what you want to trade: politics and crypto-adjacent events tilt toward Polymarket's international book; economics, temperature, and US sports tilt toward Kalshi. Traders with access to both run them side by side and watch for divergence on the same event.
Regulatory structure
Kalshi is a CFTC-regulated Designated Contract Market. Every contract listed is a registered event derivative, settled on the cash market under federal oversight. Customer funds are segregated at a qualified custodian. Customer data is subject to US regulatory protections.
Polymarket is two separate businesses. Polymarket US is a CFTC-designated contract market with NFA oversight that settles off-chain in dollars and requires full KYC — live to US traders since December 2025 following the QCEX acquisition and a September 2025 CFTC no-action letter. The international book operates on a global USDC base layer through a non-custodial protocol, is self-custodied and publicly viewable on-chain, and is closed to US persons. They do not share liquidity, settlement, or an order book.
For risk profile, the two products are different animals. Kalshi looks like a regulated derivatives exchange with segregated customer funds. Polymarket looks like a crypto protocol with centralized matching. If regulatory protection matters to you, Kalshi is the cleaner answer.
Fees and costs
| Cost | Kalshi | Polymarket |
|---|---|---|
| Trading commission (retail) | $0 | 0.10% taker |
| Funding / deposit | Free (ACH, wire, card) | USDC only — gas applicable |
| Spread cost | Narrow on liquid markets | Wider on long-tail markets |
| Winner limits | None | None |
| Account minimum | None | None |
In practice, Kalshi is cheaper per trade for most retail flow. Polymarket's 10 bps taker fee is small in absolute terms but adds up on high-frequency strategies, and the USDC-only funding rail adds friction for fiat-first traders.
Market depth and liquidity
Polymarket has a larger total catalog of open markets and deeper liquidity on marquee events — 2028 election contracts, Champions League soccer, crypto price targets. If you want to trade a $500K position on a major political market, Polymarket usually has the book depth.
Kalshi's depth is concentrated in its priority verticals: Fed rate decisions, CPI prints, jobs reports, NFL game outcomes, city temperature contracts, World Cup 2026. Retail-scale positions clear without slippage; institutional-scale positions depend on the specific market.
For day-to-day retail trading, both platforms are generally liquid enough. For strategies that need to move seven-figure positions, the choice depends on the specific market.
US access
Kalshi — legal in all 50 US states. Sign up, fund via ACH or card, start trading. The State Availability Map confirms Kalshi coverage everywhere in the US.
Polymarket — open to US traders since December 2025, but through a separate venue. Polymarket US is a CFTC-regulated exchange requiring full identity verification, settling in dollars off-chain, with availability that varies by state and a narrower market slate. Polymarket's original international book still runs on-chain and is still closed to US persons. The two do not share an order book, so the same event can price differently on each. Full breakdown in the Polymarket US guide.
Sports coverage
Kalshi's sports expansion accelerated through 2025–26. As of May 2026 the active sports book includes NFL game lines (18 weeks plus playoffs), NBA series and championship markets, MLB game and division contracts, college football, tennis majors, and a World Cup 2026 catalog that has grown past 200 individual market lines covering group stage, knockouts, top scorer, and Golden Boot. Pricing tracks sportsbook implied probability minus the vig.
Polymarket has strong championship-level and global-football markets, and it is often the deepest book for Champions League, Premier League, and international tournament futures. Day-to-day US sports game lines are thinner than Kalshi.
For a US-based sports trader, Kalshi is the default. For global soccer, Polymarket frequently has the best price.
Politics and macro
Polymarket still carries the largest political-markets book globally — 2028 cabinet appointments, election margin markets, legislative outcome contracts. If you want maximum political catalog depth, Polymarket wins.
Kalshi's political markets are narrower but have the advantage of being accessible to US residents and the depth of the CFTC regulatory framework. For economic markets — Fed decisions, CPI, unemployment, GDP — Kalshi is clearly deeper and more consistently priced.
Cross-platform arbitrage
When a version of the same event trades on both Kalshi and Polymarket, the prices frequently diverge by 5–15 percentage points. These gaps are exploitable — cross-platform arbitrage captures the discrepancy as profit regardless of the underlying outcome.
The Arb Scanner tracks matched pairs in real time and uses symmetric KL divergence to flag the ones where the gap is meaningful enough to act on. For a two-platform trader outside the US, this is one of the most reliable sources of edge in the space.
The bottom line
Choose Kalshi if you want the broadest US-listed slate, coverage in all 50 states, regulated custody, a clean retail experience, or you focus on economics, temperature, and US sports.
Choose Polymarket if it lists a contract Kalshi does not, you want maximum political and crypto-market depth, or you run global-soccer strategies — via Polymarket US if you are a US trader and your state is covered, or the international book if you are not a US person.
Run both if you are serious about edge. Cross-platform arbitrage between Kalshi and Polymarket is one of the rare strategies where a real mathematical gap shows up repeatedly — just note which of the two Polymarket books a quoted price came from, because they are not interchangeable.
For most US readers of this site: open Kalshi first, learn the platform, build the base rate scanner and EV calculator habit. Then add Polymarket US as a second venue and check it whenever Kalshi does not list the contract you want — the two books drift, and that drift is where the cross-platform edge lives.
Compare against the other US-accessible platforms: Kalshi vs DraftKings and FanDuel vs Kalshi cover the regulated sportsbook-style alternatives. DraftKings vs Polymarket walks through the sports-and-politics overlap. Pricing a Kalshi-vs-Polymarket arb or a multi-leg trade? The Kalshi parlay calculator handles joint probability and break-even in cents.